1. Field
The present invention relates to disk drives for computer systems. In particular, the present invention relates to calibrating a defect scan parameter for a disk drive.
2. Description of the Related Art
The disk in a disk drive is coated with a magnetic material which is magnetized with a write element (e.g., a write coil) in order to record information onto the surface of the disk. Various influences may render portions of the disk surface unusable (i.e., defective), for example, if the magnetic coating is not evenly applied to the disk surface or if a particle contaminates the magnetic coating. During a manufacturing “defect scan” procedure, the defective areas of the disk are located and “mapped out” so they are not used during normal operation. The defect scan typically entails writing a high frequency pattern (e.g., a 2T pattern) to the disk, and then reading the high frequency pattern while monitoring a quality metric, such as an amplitude of the read signal, a mean-squared-error of the read signal, a bit error of the read signal, a timing error of the read signal, or the output of defect scan filters having impulse responses matched to defect signatures. If the quality metric falls below a predetermined defect scan threshold, a defect is detected.
The disk is typically formatted to comprise a plurality of radially spaced, concentric data tracks each comprising a number of data sectors, wherein the defect scan maps defective data sectors to spare data sectors. If a defective data sector is not detected during the defect scan procedure, there is a risk of catastrophic data loss, either immediately, or over time as the uniform alignment of the magnetic grains deteriorates (magnetic entropy). Conversely, if the defect scan threshold is set too low in an attempt to detect more defective data sectors, more good data sectors will be identified as defective and mapped out unnecessarily, thereby reducing the capacity and performance of the disk drive.
There is, therefore, a need to improve the defect scan procedure of a disk drive by reducing the chance of missing defective data sectors without significantly increasing the number of good data sectors identified as defective.